1. Field of the Invention
This invention relates to an improved full-function brake valve for use in fluid pressure braking systems primarily employed on the semi-trailers of heavy-duty highway tractor-trailer vehicle combinations. More specifically, it relates to a full-function brake valve which combines the functions of, and replaces, multiple separate brake valves on highway semi-trailers, including tandem axle semi-trailers, with concomitant advantages.
2. Discussion of the Prior Art
To meet all of the emergency and service requirements of modern heavy-duty highway tractor-trailer combinations, while meeting all of the pertinent governmental regulations, including Federal Regulation FMVSS 121 (Docket 90-3, Notice 2), the trucking industry has resorted to a number of semi-trailer brake valve arrangements which have led complexity, high costs, installation and maintenance difficulties and related problems. These valve arrangements include multiple valves with multiple complex inter-connections, all designed to carry out multiple requisite brake functions.
As an example of one feature of such multiple installations, a pressure protection valve may be employed on the semi-trailer to maintain pressure in the air supply line from the tractor to the semi-trailer in the event that the pressurized air reservoir (tank) on the semi-trailer fails. As a related example, a one-way check valve arrangement may be employed on the semi-trailer to prevent venting of the pressurized air in the semi-trailer reservoir through the air supply line from the tractor.
As another example, a spring-brake control valve may be employed in the semi-trailer braking system to control the supply of pressurized air to the spring brakes to release them and also to exhaust air therefrom when the spring brakes are to be again applied. The brake system, however, must be designed so that the spring brakes are not released prematurely, that is, prior to pressurization of the reservoir. Safety considerations dictate that the service brake function be enabled by such reservoir pressurization prior to release of the spring brakes.
As still another example, a separate one-way check valve may be employed to control or limit the flow of pressurized air from the spring brakes and the spring brake control valve in the event of a failure of the semi-trailer pressurized air reservoir. This one-way check valve prevents the premature application of the spring brakes in the event of such failure so that the semi-trailer can continue to be towed to a safe parking place.
In addition to all of the above, a semi-trailer braking system typically employs a multi-port relay valve to control the operation of the service brakes, that is, the valve supplies pressurized air to, maintains pressurized air in, and releases pressurized air from, the service brake chambers, pursuant to control signals received from the tractor. For such control purposes, a separate pressurized control line runs from the tractor to the relay valve on the semi-trailer.
Another feature which is desired in a modern braking system is anti-compounding brake force protection. This feature protects against the undesired simultaneous application of both service brake forces and spring brake forces under certain circumstances.
Manifestly, the various valve installations and interconnections to accomplish all of these functions on a modern tandem semi-trailer are complex, costly, difficult and inconvenient to install, troubleshoot, service and maintain and otherwise are undesirable from a parts inventory standpoint. Previous efforts to integrate the various valve requirements within a single envelope or housing have not resulted in brake systems meeting current requirements.
Illustrative of the prior art is Gross et al. U.S. Pat. No. 4,915,456 and patents cited therein, i.e., Ury U.S. Pat. Nos. 4,042,281, 4,080,004 and 4,163,585; Tannin U.S. Pat. No. 4,182,535; and Carton et al. U.S. Pat. Re. 30,205 (Reissue of U.S. Pat. No. 3,992,064. Still other illustrative prior art includes Fannin U.S. Pat. No. 4,472,007 and Campanini U.S. Pat. No. 4,593,954 and the patents cited therein. None of these patents disclose or suggest a complete full-function valve, all housed within a single envelope and meeting the current requirements provided by the present invention.